Nowadays, multi-layer circuit boards having at least two circuit layers usually have a conductive through hole structure, and the conductive through hole structure is electrically connected to two of the circuit layers in the multi-layer circuit board, such that the circuit layers are electrically conducted. Currently, most of the methods for forming the conductive through hole structure are firstly utilized the mechanical and etching methods to form through vias, and then the conductive through hole structure is completed by a plating through hole (PTH).
Generally speaking, if a mechanical drilling method is applied to form the through vias, the aperture of the formed through vias will be larger, which are not suitable for mass production. If the etching method cooperated with the mechanical drilling method is applied to form the through vias, firstly, the step of photoresist coating, exposure, development and etching will be performed twice to copper foil layers located on the two opposite surfaces of a resin layer, and then openings are formed on the copper foil layers so as to form through holes penetrating through the resin layer at the locations of the openings by the mechanical drill. Although the through vias formed by such method have smaller aperture, the step of photoresist coating, exposure, development and etching will have to be performed twice to form the openings on the copper foil layers, so that the manufacturing steps are more complicated. Thus, improving the manufacture of the substrate structure having the through hole structure so as to further reduce the manufacturing steps and enhance the production yield, is currently one of the major issues needed to be overcome.